The present disclosure relates to a switching element drive circuit that provides a control terminal of a switching element with a drive signal to drive the switching element.
A switching element such as an FET (Field Effect Transistor) and an IGBT (Insulated Gate Bipolar Transistor), for example, operates when a drive signal is provided so as to generate a potential difference between a gate terminal (control terminal) and a source terminal. A parasitic capacitance is present between the gate terminal and the source terminal of the switching element, and a power loss is caused when the parasitic capacitance is charged. The power loss is proportional to the switching frequency. Therefore, as the switching frequency becomes higher, the power loss for the drive circuit which drives the switching element becomes larger, which may cause a detriment such as an increase in size of the circuit or a power source for the drive circuit.
Japanese Patent Application Publication No. 3-60360 discloses a gate drive circuit that includes a parallel resonance circuit in order to suppress an influence of a parasitic capacitance. The gate drive circuit includes an inductor that constitutes a parallel resonance circuit with the parasitic capacitance, and includes a rectification circuit that determines the direction in which a current is applied such that a charge flows back and forth between the inductor and the parasitic capacitance. The rectification circuit includes a switch (switching element) that controls application and blockage of the current (for the above, see FIG. 1 etc. of Japanese Patent Application Publication No. 3-60360). A similar configuration is also described in United States Patent Application Publication No. 2012/0176176 A1. In such gate drive circuits, basically, energy is exchanged between the parasitic capacitance and the inductor to relieve the power loss.
The drive signal according to Japanese Patent Application Publication No. 3-60360 is a positive and negative bipolar signal that has symmetric positive and negative potentials with respect to a reference potential. In some elements such as a MOSFET that uses silicon carbide (SiC), however, the voltage resistance to a negative potential with respect to a reference potential is lower than the voltage resistance to a positive potential. Therefore, in the case where a SiC-MOSFET is driven using such a positive and negative bipolar drive signal, a positive and negative bipolar signal that has asymmetric positive and negative potentials with respect to a reference potential may be required. Since the drive signal according to Japanese Patent Application Publication No. 3-60360 is a positive and negative bipolar signal that has symmetric positive and negative potentials with respect to the reference potential, a current that flows back and forth between the parasitic capacitance and the inductor is substantially uniform (see FIG. 3 of Japanese Patent Application Publication No. 3-60360, for example). In addition, the power and the current consumed by a positive power source and a negative power source that constitute a power source for drive pulses are also substantially the same.
In the case where the drive signal is a positive and negative bipolar signal that has asymmetric positive and negative potentials with respect to the reference potential, on the other hand, the current which flows back and forth between the parasitic capacitance and the inductor is also non-uniform. In the case where the power source for drive pulses is a positive and negative bipolar power source, in addition, the power and the current consumed by the positive power source and the negative power source are also non-uniform. Therefore, while a certain effect in relieving the power loss may be obtained, a load on a drive circuit that drives the switching element or a power source that supplies power to the drive circuit may be increased. In addition, it may be necessary to use a component with a high proof stress that matches the magnitude of the consumption current, or the procurement cost may be increased because of use of components with different specifications between the positive side and the negative side. Furthermore, an unintentional undershoot or the like may be generated in the waveform of the drive signal for the switching element, and may exceed the voltage resistance of the gate terminal (control terminal) of the switching element to be driven.